Which is a chemical change?

Which is a chemical change?

• A. Ice melting.
• B. Water boiling.
• C. Rust forming on iron.
• D. Sugar dissolving in water.

Answer: (C)

A chemical change happens when a substance becomes a new substance with different properties. Rust forming on iron is an example because iron reacts with oxygen (and often water) to form iron oxide, a material with its own distinct properties. That change involves forming new bonds and a new substance, and it isn’t easily reversible by simply heating or melting the iron alone. Ice melting is just a change of state from solid to liquid; the substance is still water. Water boiling is another state change, from liquid to gas, again the same substance. Sugar dissolving in water is a physical process where the sugar disperses into the water but the substances remain the same overall; no new chemical substance is formed. So rusting stands out as the chemical change.

A chemical change happens when a substance becomes a new substance with different properties. Rust forming on iron is an example because iron reacts with oxygen (and often water) to form iron oxide, a material with its own distinct properties. That change involves forming new bonds and a new substance, and it isn’t easily reversible by simply heating or melting the iron alone.

Ice melting is just a change of state from solid to liquid; the substance is still water. Water boiling is another state change, from liquid to gas, again the same substance. Sugar dissolving in water is a physical process where the sugar disperses into the water but the substances remain the same overall; no new chemical substance is formed. So rusting stands out as the chemical change.